With the demands in speeding-up, miniaturization or the like of copy machines and laser printers in the recent years, various external additives are used for the purpose of improving fluidity or triboelectric chargeability of a toner.
For example, JP-A-2010-20024 (US-A-2010-009282) discloses that a toner containing a composite oxide having a core-shell structure in which a core portion contains titanium oxide and a shell portion contains silicon oxide, wherein titanium oxide is contained in an amount of from 80 to 95% by weight serves to suppress background fogging or soiling of a charging roller.
JP-A-2002-182424 discloses that a toner containing fine metal oxide particles having a core-shell structure in which a core layer is made of a metal oxide selected from titanium dioxide, aluminum oxide, and zinc oxide, and a shell layer is made of silica, the fine metal oxide particles having an average particle size of from 10 to 30 nm and a degree of spherocity of from 1 to 1.3 is free from background fogging, faded print, and filming and the like, and has excellent durability, thereby exhibiting a high optical density.
JP-A-2004-177747 discloses that a toner containing silica-coated metal oxide particles having a core-shell structure in which a core layer is made of a metal oxide selected from titanium dioxide, aluminum oxide, and zinc oxide, and a shell layer is made of silica, and fine silica particles having a volume-average particle size of from 5 to 20 nm, has excellent cleanability and gives excellent image quality.
WO 2009/084184 (US-A-2010-330493) discloses that a toner containing surface-modified, fine composite oxide particles comprising silica-titania composite oxide particles produced by a vapor phase method, subjected to a surface treatment has a small change in triboelectric charges with the passage of time.
JP-A-2010-72569 (US-A-P2010-075242) discloses that a toner containing a resin binder containing a polyester obtained by polycondensing an alcohol component and a carboxylic acid containing isophthalic acid, and an external additive containing fine silica particles containing a metal or a metal oxide has excellent durability and triboelectric chargeability, so that stable fixed images are obtained for a long period of time.
JP-A-2001-51448 discloses that a toner containing a polyester resin containing a composition having an acid value of 6 mgKOH/g or more, and containing isophthalic acid in an amount of from 25 to 50% by mol, and terephthalic acid in an amount of 8% by mol or less, has excellent low-temperature fixing properties, has little generation of fusion to a developer roller and a blade, scattering, background fogging, or the like in long-term continuous copying, and can realize stabilized image properties.